Photoresist Deposition Research Articles

Design and Fabrication Considerations for Thermo-Resistive Pixel Detectors for Room Temperature Directional Long Wavelength IR Sensing

Rapid growth in application demands for smart sensing has fostered the development of micro-electromechanical-based devices with unique capabilities. Recent developments have led to complex autonomous systems that require a variety of intelligent sensing tasks to render human-machine interactions safe and efficient in workplace environments comprising both a human and robotic workforce. Here we report the design and fabrication of a novel thermo-resistive LWIR detector, for sensing and recalculating the direction of incident LWIR radiation for potential robotic applications. The work employs standard silicon micromachining processes along with sol-gel chemistry to fabricate three-dimensional pixel detectors to approximate an LWIR source's direction of incidence using thermo-resistive material. There have been no prior reports of the thermo-resistive effect in conjunction with directionality in LWIR sensors. In addition to the fabrication process flow, we describe the mathematical framework for sensor operation and present a photoresist deposition process for large 3-D topographic surface structures. We discuss the advantages and challenges of the currently designed and fabricated prototypes and highlight issues that limit their angular LWIR response.

Comparison of Conventional and Maskless Lithographic Techniques for More than Moore Post-Processing of Foundry CMOS Chips

This article details and compares the technology options for post–processing foundry produced CMOS at chip-scale to enable More than Moore functionality. In many cases there are attractions in using chip-based processing through the Multi-Project Wafer route that is frequently employed in research, early-stage development and low-volume production. This article identifies that spray-based photoresist deposition combined with optical maskless lithography demonstrates sufficient performance combined with low cost and operational convenience to offer an attractive alternative to conventional optical lithography, where spin-coated photoresist is exposed through a patterned photomask. [2020-0249]

A cost-efficient approach for simultaneous scanning electrochemical microscopy and scanning ion conductance microscopy

A novel and cost-efficient probe fabrication method yielding probes for performing simultaneous scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) is presented. Coupling both techniques allows distinguishing topographical and electrochemical activity information obtained by SECM. Probes were prepared by deposition of photoresist onto platinum-coated, pulled fused silica capillaries, which resulted in a pipette probe with an integrated ring ultramicroelectrode. The fabricated probes were characterized by means of cyclic voltammetry and scanning electron microscopy. The applicability of probes was demonstrated by measuring and distinguishing topography and electrochemical activity of a model substrate. In addition, porous boron-doped diamond samples were investigated via simultaneously performed SECM and SICM.Graphic abstract

2D periodic structures patterned on 3D surfaces by interference lithography for SERS

This contribution brings novel concept of Ag islands formation in 2D periodic arrangement with square symmetry on special 3D surfaces – gallium phosphide (GaP) nanocones, for surface-enhanced Raman spectroscopy application. 2D periodic structure in square symmetry with period of app. 470 nm is patterned in photoresist layer by interference lithography using double exposure of a two-beam interference optical field. Two different techniques for photoresist deposition on 3D surface are compared: spin-coating and photoresist deposition from water level. After Ag sputtering and lift-off, GaP nanocones are decorated with Ag islands in 2D periodical arrangement. Detectable enhancement in Raman signal for Rhodamine 6G adsorbed on prepared samples is demonstrated.

Deposition of Ultra-Thick Photoresist by Thin Film Multi-Layer Spray Coating

Deposition of Ultra-Thick Photoresist by Thin Film Multi-Layer Spray Coating

Development of High-Sensitive Detection System for Redox Analytes Having a Standard Potential Higher Than O2 Evolution by Using Micropatterned Conductive Boron-Doped DLC Electrodes

1. Introduction Recently, cobalt, manganese and cerium are widely used in mass-produced products such as a lithium ion battery. It has been reported that the excessive consumption of these metal ions causes various diseases like neurotoxicity. In industrial wastewater discharge standards, Co2+, Mn2+ and Ce3+contents of wastewater has been regulated below several micro-molar. These redox species are generally analyzed using photochemical method. Some time, however, is required for analysis using the method and initial measures cannot be taken promptly when problems such as the content of metal ions exceeding the discharge standard occur. Therefore, electrochemical monitoring system which can shorten time of analysis should be developed. The standard potential of Co2+, Mn2+ and Ce3+ are higher than that of O2evolution potential. Redox reactions of these analytes cannot be observed at conventional metal electrodes. In this study, boron-doped diamond-like carbon (B-DLC) [1] with higher overpotential for O2evolution was selected as the electrode that redox reaction of the analytes can be observed. The detection limit of Ce3+ (model analyte) at a flat-disk electrode of B-DLC was 39 mM. Our research group tried to fabricate interdigitated microarray electrodes (IDA) because it shows one or two orders of magnitude higher sensitivity than that of the flat-disk electrode. IDA are composed of two sets of microband array neighbored (called generator and collector). The potential of one microband pairs (collector) is set at reduction potential of redox analyte, and that of the other is swept toward oxidation potential (dual mode). Redox cycling occurs between two sets of the microband pairs. The generator exhibits higher amplification of oxidation current by redox cycling compared to the current without applying the potential on the collector (single mode). We have reported that B-DLC-IDA with 2 mm/2 mm of bandwidth/gap exhibited ca.10 times amplification factor corresponding to the theoretical value [2]. The amplification factor of Ce3+, however, was half of the theoretical value. As a result, the detection limit was 8.8 mM. The reduction of Ce4+ is not promoted at the collector because the sample solution is a reductant. Moreover, Ce3+generated at the collector is hardly supplied to generator by diffusion, which causes inefficient redox cycling. When the collector is set at an oxidation potential, Ce3+ are constantly supplied to the collector by nonplanar diffusion. Ce4+generated at the collector is considered to be supplied to the generator at a higher diffusion rate. In this report, amplification factor of Ce3+was tried to be improved by changing the potential set at the collector. 2. Experimental B-DLC was synthesized on quartz substrates with RF plasma CVD method using a mixed solution of n-hexane and trimethyl borate as a source material. RF power was 175 W and the deposition time was 40 minutes. The alminium pattern of IDA was fabricated by the lift-off technique using photoresist and alminium deposition. Alminium on B-DLC-IDA was removed in a sodium hydroxide solution after O2plasma etching of B-DLC. The structure of B-DLC-IDA was designed to be 65 pairs of microbands with a length of 200 μm and bandwidth/gap of 2.0 mm. Single-dual mode measurements were carried out using the B-DLC-IDA in 1 mM Ce(NO3)3 + 0.1 M HNO3solution. 3. Results and discussion Figure1 shows the optical micrographs of the B-DLC-IDA. The bandwidths and gaps were observed to be 1.96 and 2.04 mm, respectively. The deviation between the actual gap and the designed value was less than 2%. Raman spectra of B-DLC were identical before and after the processing of IDA. It was confirmed that amorphous structure and composition ratio of sp2/sp2+sp3 (= 75%) in B-DLC did not change during IDA processing. The working potential range in 0.1 M sulfuric acid was constant after IDA processing. These results suggest that the redox reaction of Ce3+can be served at the B-DLC-IDA. In the dual mode of Ce3+, the potential of the collector was set at 1.37 V, and the potential of generator was swept from 0.8 to 1.7 V. Amplification factor closed to the theoretical value could be obtained. The detection limit of Ce3+was decreased from 8.8 to 4.4 mM by changing the applied potential of the collector from 1.25 to 1.37 V. 4. Summary Fabrication of the B-DLC-IDA and optimizing method of electrochemical measurement can establish highly sensitive electrochemical system that can analyze redox species with a standard potential higher than O2evolution. 5.

Methods of Patterned Mist Deposition of Nano-Crystalline Quantum Dot Films

This study extends an investigation concerned with patterning of ultra-thin films formed by means of mist deposition technique using colloidal solutions of nanocrystalline CdSe nanodots with ZnS shell suspended in organic solvent. The CdSe/ZnS nanocrystalline quantum dots (NQD) show very good promise in display/LED and variety of nano-labeling and counterfeiting applications between others.Regardless of application, to become a part of the functional device the NQD film must be patterned accordingly. The conventional top-down patterning sequence involving photolithography and etching cannot be used in this case as the process would results in the critical damage to the NQD film. Hence, alternative patterning technologies must be pursued. The goal of this contribution is to review past experiments and to introduce new approach to NQD film patterning in conjunction with mist deposition technology.In this study NQDs deposited were CdSe/ZnS core/shell NQDs featuring average diameter of 6.5 nm and corresponding red (620 nm) emission wavelength. The method of mist deposition converts colloidal solution, in this case CdSe/ZnS NQDs suspended in toluene, into a fine mist of sub-micrometer sized particles using an atomizer. The mist droplets are carried from the atomizer to the deposition chamber by ultrapure N2 carrier gas and then coalesce on the substrate in the presence of an electric field.Patterned deposition using mechanical masks of nanocrystalline quantum dot (NQD) films by means of mist deposition on various substrates was demonstrated earlier (e.g. [1]). The process can be used for the variety of purposes including security labeling, barcode printing as well as in photonic detection/conversion device fabrication. In the continuation of this investigation the feasibility of patterned mist deposition of NQD films by surface functionalization applied prior to mist deposition instead of the use of mechanical masks during deposition was explored. With this approach desired pattern can be created through the bottom-up process by properly functionalizing SAM material prior to NQD film formation by mist deposition. Surfaces of substrates used in this experiment, including Si wafers and laboratory glass were functionalized by immersion in trichloro (1H,1H,2H,2H-perfluorooctyl) silane (FOTS) and let dry in an ambient air. UV exposure was carried out in ambient air and at room temperature using apparatus equipped with low-pressure mercury lamp featuring intense 185 and 254 nm wavelengths. Further modifications of the SAM material were accomplished by means of the lamp-based rapid optical surface treatment (ROST) at the temperatures up to 300 oC. In terms of selectivity of deposition the results obtained in this study were strongly affected by the modification of wetting properties of the surface by the presence of electric field accelerating process of mist deposition. This effect, known as electrowetting, was influencing FOTS surface wettability and preventing selectivity of the deposition process. The effect can be partial reversed with the low-temperature thermal treatment in ambient air. The manipulation of the surface wettability of FOTS using UV light, electric field and temperature process is employed to alter selectivity of the NQD film deposition process.In the extension of this investigation, approach to NQD CdSe/ZnS film patterning based on the principles of a lift-off process is investigated. In this case a negative image of the final NQD pattern is created by means of photolithography in the layer of photoresist and blanket mist deposition of NQD film follows. Subsequently, patterned photoresist is oxygen plasma ashed lifting off NQDs from the resist covered areas and leaving them in the areas not covered with photoresist.The overall results obtained in this study demonstrate that, unlike other thin film deposition methods using colloidal solutions such as spin-on or micro-spray, mist deposition is compatible with a range of film patterning scenarios. In the full account of this work a complete set of experimental results obtained in the course of this investigation is presented and possible applications of the processes under investigation considered.

Fabrication of TiO2 micro-structures by cathodic deposition

Fabrication of TiO2 micro-structures by combining photolithography with SU-8 photoresist and electrochemical cathodic deposition method was firstly demonstrated in this study. Diameter of the fabricated circular TiO2 micro-structures was ranged from 50 to 125μm, and surface morphology of the TiO2 was found to be porous. Shape of the micro-structures obtained is determined by shape of the SU-8 template prepared, therefore, it can be easily controlled by photolithography conditions. Morphology and crystal structures of the TiO2 micro-structures can be controlled by electrochemical parameters. Therefore, this result demonstrated the possibility to control properties of TiO2 micro-structures fabricated and the potential to improve performance of TiO2 micro-structures in applications.

X-ray-Initiated Metal-Promoted Thin Film Growth

In many applications, the deposition of solid films requires control over thickness, conformality, and possibly spatial resolution. Polymeric films are often grown on surfaces with the aid of X-rays or other excitation sources,one example being the deposition of photoresist masks. Polymerization is also possible via the use of catalysts, typically metalorganic compounds based on early transition metals. Here we report on a way to grow solid films by combining X-ray excitation with early transition-metal promotion, for the particular case of the polymerization of pentakis(dimethylamido)tantalum (PDMAT) on a tantalum foil initiated by radiation with soft X-rays (Al Kα radiation, hν = 1486.6 eV). Detailed mechanistic studies led to the conclusion that the initial excitation is triggered by the secondary electrons generated from the underlying surface and that activation is propagated to form polymeric films with the help of the tantalum atom in the metalorganic precursor. This dual-functionality polymerizati...

Improving Photoresist Spray Coating on 3D Structures for Microfluidic Devices

ABSTRACTSpray coating of a photoresist onto three-dimensional (3D) structure was investigated. To improve the uniformity of photoresist deposition onto the 3D structure, a shield plate with an aperture was used. The shield plate set over a sample permitted the resist deposition on the sample surface located in the aperture area while the plate blocked the deposition for the other area. The spray flow which is suitable for the resist deposition can be used effectively. Numerical analysis revealed that the vertical velocity component of gas flow was enhanced in the aperture area. In the experiments of the spray coating, the difference between the resist film thicknesses deposited on top and bottom trench surfaces was decreased. On the trench sidewall, resist bump formation, which was frequently observed in spray coating, was suppressed. The uniform resist deposition is necessary to realize 3D microdevices by lithography. In the microfluidic devices of dielectrophoresis, aside from the top and botttom trench surfaces, the trench sidewall can be used to fabricate device structures such as electrode for dielectrophoresis.

Area-Selective Polymer Deposition on Micro-Area Framed by Trenches with Falling Liquid Film

Additional formation of functional films on the defined micro-areas on the microstructure is often complicated and need advanced control technique. Any simple and faster deposition processes are favorable. In this paper, we propose a simple processing method to form thin films on the defined areas by falling dispersion liquid containing the coating materials on a tilted silicon substrate with trench frames. We attempted to hold the coating solution and to form a thin film within the framed micro-area. We fabricated 500 nm-wide trench frames on silicon substrates, and flew a diluted photoresist (PR) solution, as the coating solution, on the tilted surface with the frames. PR film was successfully formed on the framed area for the substrate modified with hexamethyldisilazane (HMDS). However, the area-selective PR deposition was difficult in case the substrate was not treated with HMDS. It is likely that lower contact angle for the substrate without HMDS treatment is unfavorable for the area-selective PR deposition for the excess adhesive properties of the coating solution to the surface. The effectiveness of the frames as the guide to hold a liquid droplet within the defined area was considered.

Electroplated Metal Buried Interconnect and Through-Wafer Metal-Filled Via Technology for High-Power Integrated Electronics

In this paper, we present the design, fabrication process, and experimental results of an electroplated metal buried interconnect and through-wafer via technology suitable for extremely low resistance interconnection of microelectronic devices. The technology is demonstrated using a 3-D daisy-chain test structure comprised of electroplated through-wafer vias buried in the silicon substrate to form the respective interconnect. In contrast to the conventional daisy-chain structures used in flip chip joining and packaging, the designed structure is fabricated on a single substrate without requiring a subsequent bonding process. The top connectors formed on the front-side of the substrate are connected to bottom connectors buried inside the substrate (buried interconnects) through 61-mum-high, void-free, fully-filled, electroplated vias. The metal electroplated buried interconnects are fabricated at the bottom surface of 232-mum-deep trenches formed on the backside of the substrate. Processes for forming deep trenches with rounded-off edges and photoresist spray coating have been developed to fabricate the buried interconnects and complete the daisy-chain structure. Developed processes enable conformal photoresist deposition inside the deep vertical trenches with excellent step and sidewall coverage, surpassing the limitations of conventional fabrication approaches. Furthermore, electroplating molds were perfectly patterned at the bottom of these deep trenches. Through-wafer vias with controllable height are fabricated by direct bottom-up plating from the buried interconnect without additional preparation, such as wafer bonding or hole filling processes. The interconnection scheme developed in this research considerably reduces the height of narrow vertical vias, compared to conventional through-wafer vias, and enables a high density array of interconnect structures. Moreover, low resistance interconnect suitable for high power applications can be realized with thick electroplated copper and fully-filled vias. Buried interconnect can be also utilized in high voltage transistor applications. Resistance testing has been performed to validate the electrical integrity of the fabricated daisy-chain structure, and the results are compared with simulation and analytical calculations.

Large Area Flexible Electronics Fabrication by Selective Laser Sintering of Nanoparticles with a Scanning Mirror

AbstractThe development of electric circuit fabrication on heat and chemically sensitive polymer substrates has attracted significant interest as a pathway to low-cost or large-area electronics. We demonstrated the large area, direct patterning of microelectronic structures by selective laser sintering of nanoparticles without using any conventional, very expensive vacuum or photoresist deposition steps. Surface monolayer protected gold nanoparticles suspended in organic solvent was spin coated on a glass or polymer substrate. Then low power continuous wave Ar-ion laser was irradiated as a local heat source to induce selective laser sintering of nanoparticles by a scanning mirror system. Metal nanoparticle possessed low melting temperature (<150°C) due to thermodynamic size effect, and high laser absorption due to surface plasmon mode. These make metal nanoparticles ideal for the low temperature, low laser energy selective laser processing, and further applicable for electronics fabrication on a heat sensitive polymer substrate. We extended our laser selective sintering of nanoparticles research to a large area (> 4” wafer) using scanning mirror to demonstrate current technology for industry level fabrication.

Electrospray Deposition of Photoresist: A Low Impact Method for the Fabrication of Multilayered Films

Electrospray deposition has been investigated as a substitute for photoresist spin coating. The morphology of Microposit S1813 photoresist films has been studied as a function of several spray conditions including resist concentration, substrate surface, and flow rate. Film morphology is controlled by three process parameters: the surface energy determines the equilibrium conditions of resist on the substrate; the viscosity and volume flux determine the relaxation time for the depositing resist solution after impact on the substrate. Electrosprayed photoresist films have been used for photolithographic patterning and it has been demonstrated that electrospray deposition is an effective method for deposition of photoresist on top of fragile, thin films, which can be used for multilayered thin film fabrication.

Enhancing the stability of kinesin motors for microscale transport applications

Biomolecular motors, such as kinesins, have great potential for micro-actuation and micro- or nanoscale active transport when integrated into microscale devices. However, the stability and limited shelf life of these motor proteins and their associated protein filaments is a barrier to their implementation. Here we demonstrate that freeze-drying or critical point-drying kinesins adsorbed to glass surfaces extends their lifetime from days to more than four months. Further, photoresist deposition and removal can be carried out on these motor-adsorbed surfaces without loss of motor function. The methods developed here are an important step towards realizing the integration of biological motors into practical devices, and these approaches can be extended to patterning and preserving other proteins immobilized on surfaces.

Characteristics of HfO2 and SiO2 on p-type silicon wafers using terahertz spectroscopy

The effect of high-κ dielectric HfO2 films on 200 mm diameter p-type silicon substrates was investigated and compared with conventional dielectric material, SiO2. We employed all-optical characterization methods using terahertz (THz) time-domain spectroscopy and visible cw pump/THz probe spectroscopy. Measurements were performed on two sets of samples, each set containing both HfO2 and SiO2 coated wafers with varying thickness of oxide layer. One set had a protective coating of either photoresist or Si3N4 deposition above the oxide layer which in turn was on a heavily doped p+ layer on p-type silicon. The samples exhibited similar linear transmission in the THz frequency range studied. However, when using an Ar+-ion laser as an optical pump source, differential measurements (with and without the pump source) showed that the transmission was far smaller for the high-κ dielectric HfO2 films than its conventional dielectric SiO2 counterparts, indicating the presence of large photo-generated carrier density in the p-type substrate.

Droplet-based photoresist deposition

Photoresist droplets are ejected onto a wafer surface by an acoustic two-dimensional micromachined ejector array. The spread of single droplets on a silicon wafer surface at varying droplet speeds is studied. Series of photoresist droplets are printed periodically drop on demand on a silicon wafer surface and profiles of a single droplet and two droplets overlapping with varying distances of 25 and 1μm on a silicon wafer are demonstrated. Moreover, 3.4μm thick spinless full coverage of a 4in. wafer with photoresist is demonstrated which indicates a potential for coating wafers in less than a few seconds.

Deposition of thin and uniform photoresist on three-dimensional structures using fast flow in spray coating

Realizing photolithography on three-dimensional structures is useful for micromachining; however, a thin and uniform resist film is difficult to prepare on a non-planar sample. A spray coating technique has the potential to deposit a uniform and defect-free resist film on a three-dimensional structure. In this study, the characteristics of spray coating are examined focusing on spray flow speed. Faster spray flow is found to remove the pinhole defects even at the bottom of a deep cavity with a high aspect ratio. The results of patterning performance on a deep three-dimensional structure are also shown. A line-and-space pattern on a 200 µm deep groove is demonstrated to have thick and thin resist coverage at the convex and concave corners, respectively with no pinhole defects. The obtained results of the spray coated resist film are discussed based on the fluid dynamics.

Femtoliter to Picoliter Droplet Generation for Organic Polymer Deposition Using Single Reservoir Ejector Arrays

Direct deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics, has the potential to reduce waste as well as production costs. A new design of acoustically actuated two-dimensional (2-D) micromachined droplet ejector arrays can eject various solvents and other fluids ranging from femtoliter to picoliter droplet volumes. These ejectors do not harm fluids that are heat or pressure sensitive. Moreover, they are chemically compatible with the materials used in integrated circuit manufacturing. Therefore, they can be used for benign deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics. A vibrating circular Si/sub x/N/sub y/ thin-film membrane with an orifice at the center forms the unit cell of a 2-D ejector array. Initially, one side of the membrane is loaded with the ejection fluid. Then, ultrasonic waves generated by a piezoelectric transducer force the membranes to displace at resonance. As a result of this actuation, droplets are ejected through the membrane orifice. We ejected water at 1.06 MHz, isopropanol at 1.14 MHz, ethyl alcohol at 1.06 MHz, and acetone at 1.04 MHz from a 20/spl times/20 single reservoir 2-D micromachined array with 160 /spl mu/m in diameter Si/sub x/N/sub y/ membranes and 10 /spl mu/m in diameter orifices. The performance of single reservoir flextensional membrane-based ejector arrays was compared to flextensional membrane-based ejector arrays with reservoirs. A 50% decrease in the required power per ejected droplet and a reduced design complexity were demonstrated over the 2-D micromachined arrays with individual reservoirs. In addition, we deposited Shipley SPR 3612 photoresist at 1.12 MHz in a dry lab environment. No spinning was done after deposition. We covered a 2/spl times/2-mm area on a wafer with a 5.5-/spl mu/m thick photoresist layer. The maximum thickness variation over the area was 0.4 /spl mu/m. Moreover, we present a directly written 1.6-/spl mu/m thick 900-/spl mu/m wide and 8-mm long homogeneous photoresist line. The photoresist thickness variation along the line was 0.2 and 0.4 /spl mu/m in vertical and horizontal directions, respectively.

Fabrication and characterization of vertically aligned carbon nanofiber electrodes for biosensing applications

We describe recent experiments aimed at using carbon nanofibers for biosensing applications. Vertically aligned carbon nanofibers are grown on molybdenum electrodes to provide electrical contact to the nanofibers. Upon exposure to electrolyte solutions, we find that short nanofibers of < 1 μm length can be wet and dried without significant mechanical disruption. However, longer fibers are prone to clumping due to meniscus forces. Deposition of SiO 2 adds mechanical strength and electrically insulates the nanofiber sidewalls, which can be further augmented by additional deposition of epoxy-based photoresist. Reactive-ion etching re-exposes the carbon core, localizing the electrical response to the nanofiber ends and leading to electrically active electrodes of ∼ 40 nm radius. Measurements of the diffusion-limited current from ensembles of nanofibers are solutions containing redox agents are in excellent agreement with classical electrochemical theory. We also briefly describe the use of chemical and electrochemical methods to functionalize carbon nanofibers.